#include <stdlib.h>
#include <avr/io.h>
#include <util/delay.h>

int main() {
  DDRB |= (1 << PB5); // Set pin 13 to output mode
  while (1) {
    PINB |= (1 << PB5); // Set pin 13 output to 1
    _delay_ms(100);
    PINB &= ~(1 << PB5); // Set pin 13 output to 0
    _delay_ms(100);
  }
}
